Theoretical and computational studies of organometallic reactions: successful or not?

Abstract

Theoretical and computational methods are powerful in studying transition metal complexes. Our theoretical studies of C-H σ-bond activation of benzene by Pd(II)-formate complex and that of methane by Ti(IV)-imido complex successfully disclosed that these reactions are understood to undergo heterolytic σ-bond activation and the driving force is the formation of strong O-H and N-H bonds in the former and the latter, respectively. Orbital interactions are considerably different from those of σ-bond activation by oxidative addition. The transmetallation, which is a key process in the cross-coupling reaction, is understood to be heterolytic σ-bond activation. Our theoretical study clarifi ed how to accelerate this transmetallation. Also, we wish to discuss weak points in theoretical and computational studies of large systems including transition metal elements, such as the necessity to incorporate solvation effect and to present quantitatively correct numerical results. The importance of solvation effects is discussed in the oxidative addition of methyliodide to Pt(II) complex which occurs in a way similar to an S N 2 substitution. To apply the CCSD(T) (coupled cluster singles and doubles with perturbative triples correction) method, which is the gold standard of electronic structure theory, to large system, we need to reduce the size of the system by employing a small model. But, such modeling induces neglects of electronic and steric effects of substitutents which are replaced in the small model. Frontier-orbital-consistent quantum-capping potential (FOC-QCP) was recently proposed by our group to incorporate the electronic effects of the substituents neglected in the modeling. The CCSD(T) calculation with the FOC-QCP was successfully applied to large systems including transition metal elements.

Aromatic C–H σ-Bond Activation by Ni0, Pd0, and Pt0 Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism

“…An increase in the benzene LUMO population leads to an increase in the H a atomic population because the LUMO of the distorted benzene contains some antibonding C–H a character, as will be shown below. These population changes indicate that the charge transfer (CT) occurs from the Pt 5d orbital to the benzene LUMO, as discussed previously. − The electron population of the HOMO (π) of propene moderately decreases with Pt but that of the LUMO (π*) does not vary much, unlike the case for Ni, which is consistent with a propene that does not participate directly in the C–H activation (see a discussion of the propene HOMO and LUMO populations on page S9 in the Supporting Information). Similar results are obtained with Pd 0 (Figure S2).…”

“…The important orbital interaction in the usual concerted oxidative addition to metal center has been discussed in detail. − However, the orbital interaction in the ligand-to-ligand H transfer has been less discussed . It has in fact been presented for the Si–H σ-bond activation of silane by a Zr II ethylene complex. , …”

Frontier Orbitals in Transition-Metal- and Lanthanide-Mediated Reactions

“…The LUMO of CeCl 4 and PrCl 4 has a 4f orbital as the main component [for example, see LUMO (Ce)]. 32,33 The small spatial size of 4f orbitals keeps the LUMO from overlapping with the HOMO of the other molecules and reduces the kinetic instability.…”

“…However, its application to the reactions mediated by transition metal and lanthanide catalysts has rarely been documented so far. 4 The frontier orbital theory, originally developed for intermolecular reactions, cannot be directly applied to many transition-metal-and lanthanide-mediated reactions which often involve intramolecular reactions or rearrangements of intermediate complexes in the key steps.…”

A Quantum-Chemical DFT Approach to Elucidation of the Chirality Transfer Mechanism of the Enantioselective Suzuki–Miyaura Cross-Coupling Reaction

“…Since aryl-aryl bond forming cross-couplings are mechanistically quite similar, in our studies on enantioselective coupling we concentrated on the Suzuki-Miyaura reaction, which is usually applied as a method of first choice. The mechanics of the nonstereocontrolled Suzuki-Miyaura (and a few other couplings) reaction catalysed by complexes of nonchelating monophosphines has been studied in detail (Scheme 1) [20][21][22][23][24][25][26][27][28][29] and can be extrapolated to reactions catalysed by transition metal complexes of different types and to stereoselective transformations. At …”